Apparatus for the study of the small angle scattering of x-rays using an angularly displaceable detector



3,371,207 TERING Feb- 27. 1968 H. BoTTAzzI ETAL 'APPARATUS FOR THE STUDY OF THE SMALL ANGLE SCAT 0F X-RAYS USING AN- ANGULARLY DISPLACEABLE DETECTOR Flled June 28, 1965 mw/ h m NQ 4. 0

3,371,207 APPARATUS FOR THE STUDY F THE SMALL ANGLE SCATTERHNG 0F X-RAYS USING AN ANGULARLY DISPLACEABLE DETECTR Henri Bettazzi, Sainte-Foy-les-Lyon, Rhone, Albert Renouprez, Decines, Dominique Weigel, Rennes, and Marcel Prettre, Villeurbanne, France, assignors to Centre National de La Recherche Scientifique, Paris, France, a French organization Filed .lune 28,1965, Ser. No. 467,466 4 Claims. (Cl. Z50-51.5)

ABSTRACT 0F THE DISCLOSURE An X-ray goniometer for low angle scattering has a stand, an adjustable arm to support the X-ray source, and an angularly displaceable arm supporting an X-ray detector. This latter arm is frictionally driven by an endless metallic ribbon applied against a substantial portion of the periphery of a smooth cylindrical sector carried by this arm. This ribbon is supported by rollers driven through speed reducing gearing, and the drive shaft of the gearing actuates a counter.

This invention relates to an apparatus for the study of the small angle scattering of X-rays.

The study of X-ray diffusion by a sample of matter is of great value in the determination of the physical properties of the matter. Low angle scattering, i.e. the phenomena which takes place at small angles with respect to the incident rays, is of particular interest. But it is rather diliicult in .practice to obtain accurate results.

In a first type of known apparatus the beam used is quite tine and slightly divergent, its monochromatism 'being insured by appropriate filters. But the adjustment of the collimator slits is difficult and the beam is not perfectly symmetrical. In another known type of apparatus the monochromatism of the beam is obtained by reflection from a quartz plate.

The present invention relates to this second type of apparatus and it has for its object an apparatus for the study of low angle X-ray scattering, wherein a radiogoniometer or explorer arm is automatically angularly displaced about its pivot by an endless ribbon supported by rollers and which bears against an arcuate surface carried by the arm concentrically with respect to the pivot, one at least of the said rollers being rotated at a slow speed by a driving motor.

The endless ribbon is preferably made of a resilient metal and it is applied against the arcuate surface under the action of its own longitudinal flexibility. The ribbon may be supported by two rollers which are driven by a Common transverse shaft through worm-and-wheel speedreducing gearing, the common transverse shaft being itself driven by the driving motor through a third wormand-Wheel speed-reducing gearing.

In the accompanying drawings:

FIG. 1 is a general plan view of an apparatus according to this invention.

FIG. 2 is an enlarged diagrammatic plan view illustrating the general arrangement of the mechanism which frictionally drives the explorer arm.

FIG. 3 is an enlarged diagrammatic vertical section taken along line III-III of FIG. l.

The apparatus illustrated in FIG..1 comprises a thick and rigid bed or base 1 formed with appropriate grooves adapted to form guides for a number of longitudinally adjustable carriages which will hereinafter be referred to as main carriages. These grooves may for instance be of the dovetail type commonly used in machine tools. The

nited States Patent Oiitlce 33,371,267 Patented Feb. 27, 1968 bed 1 may besides be supported by appropriate feet, not illustrated, such feet being preferably adjustable in order to avoid any bending stress on the bed when sitting on an uneven supporting surface.

The bed 1 carries in the vicinity of one of its ends (left-hand end in FIG. l) a first main carriage 2 adapted to support the X-ray emitting unit. This carriage is locked on the -bed by means of bolts 3. It supports a turret head 4 provided with a central locking nut 5. This turret head is integral with an arm 6 on which is slidably mounted an auxiliary carriage 7. The latter is adapted to support the X-ray tube which has been merely indicated in dotted lines at 8. Owing to the possibilities of angular and linear adjustment by means of the turret head 4, of the auxiliary carriage 7 on the main carriage 2 and of the main carriage 2 on the bed 1, the object focus may be disposed at any position in theA plane of the axis of the X-ray tube 8.

The bed 1 supports in the vicinity of the carriage 2 a second main carriage 9 on which the monochromator unit of the apparatus is mounted. This unit comprises a nonsymmetrical arcuate quartz plate and an inlet slit adapted to limit the portion of the plate which receives the X-rays beam. The second main carriage 9 is locked on the bed 1 by bolts 10 similar to the above-mentioned bolts 3 and it supports a turret head 11 which may be angularly adjusted by means of a ditferential screw 12. This turret head 11 carries the quartz plate 13 which is retained in position by suitable means, not illustrated. The turret head 11 is formed with two vertical slits respectively for the inlet and the outlet of the X-ray beam and in front of the tirst one are disposed two blades 14 which define the width of the passage for the X-rays. These blades are preferably made of tantalum under a relatively small thickness. They are suitably secured onto the periphery of the turret head 14.

As in known apparatus the beam from the monochromator unit should pass through two accurately adjustable slit devices, the former delimiting the beam width and the second screening the undesirable rays diffused by the edges of the former. Each device comprises two tantalum blades which have been highly polished and accurately sharpened under microscopic control, these blades being movable in opposed directions with respect to each other on a small auxiliary carriage which is itself transversely movable with respect to the bed. The iirst device, which has been generally referenced 15, is supported by the second main carriage 9 itself. The tantalum blades are indicated at 16 while numerals 17 and 18 designate the knobs which control respectively the spacing apart of the blades and the transverse displacement of the small auxiliary carriage by which they are supported. The second slit device, generally referenced 19, comprises blades 20 and control knobs 21 and 22; it is mounted on a third main carriage 23 which carries the pivot of the radiogoniometer or explorer arm.

This second main carriage 23 is locked on the bed 1 by means of bolts 24. It supports an auxiliary carriage 25 which is transversely movable on the main carriage 23 by means of a hand-wheel 26. The auxiliary carriage 25 in turn supports the .pivot of the explorer arm 27 on which are respectively mounted a sample carrier 28 and a detector 29.

The sample carrier 28 is in the form of a small turret head which is secured onto the arm 27 exactly along the pivoting axis thereof. This turret head has a horizontal sleeve in which the sample may be clamped. The sample may be in the form of a solid disc, or a container for a powdered or liquid material submitted to the test, this container being preferably provided with lateral windows made of very thin beryllium. As to the detector 29 it may be a. photographic chamber, of a Geiger counter or of a scintillating device associated with a photomultiplicator. It is carried by a small support which is longitudinally adjustable on the arm 27, the latter being provided for this purpose with a slot 27a. A third slit unit 30, similar to units 15 and 19, is mounted in front of the detector, this unit comprising tantalum blades 31 and control knobs 32 and 33.

The explorer arm 27 is mounted 0n a high precision ball-bearing. It extends rearwardly beyond the end of the bed 1 and it is formed with an arcuate vertical surface 34 secured against its lower side so as to be exactly concentric to the pivoting axis of the arm on the auxiliary carriage 25. The bed 1 also has a rearward extension 35 which is disposed at a lower level with respect to the arcuate surface 34, this extension rotatably carrying two rollers 36 over which passes an endless metallic ribbon 37 which frictionally drives the said surface 34 and consequently the arm 27.

FIGS. 2 and 3 clearly show this drive gearing. In order not to overcrowd the drawing, the extension 35 of the bed 1 which carries the bearings in which the vertical shafts 38 of rollers 36 are supported has not been illustrated. Further the thickness of the ribbon 37 has been exaggerated, this ribbon being a length of a strip of spring steel, the ends of which have been brazed with each other, the junction being thereafter accurately ground in order to eliminate any overthickness, and the endless ribbon thus obtained being heat-treated to recover its original resiliency. The length of this ribbon 37 is such that when it is mounted on the rollers 36 as a transmission belt, the arm 27 being previously set aside, it is already under a noticeable tension. When the arm is thereafter returned to its normal position, the arcuate surface 34 depresses one of the portions of the ribbon 37 as indicated in FIG. 2 whereby the tension of the latter is substantially increased. The arrangement is preferably such that the ribbon 37 bears regularly against the arcuate surface 34 substantially from one roller 36 to the other. Under these conditions the reaction of the ribbon causes a high pressure of the latter against the surface 34 and when the rollers 36 are rotated, the surface is frictionally driven together with the arm 27 without any slip in normal operation (i.e. in the absence of any abnormal resistance).

On each shaft 38 is mounted a worm-wheel 39 which meshes with a worm 4t), both worms 40 being carried by a common transverse horizontal shaft 41 also rotatably supported by the extension 35 of the bed 1. This shaft 41 in turn carries a worm wheel 42. which meshes with a vertical worm 43, the shaft 44 of which is driven by an electric motor 45 through a dismountable shaft coupling 46. By appropriately selecting the speed of motor 45 (which is preferably easily removable so as to be easily changed when desired), it is possible to realize for the arm 27 any angular velocity desired, no matter how slow it may be.

The vertical shaft 44 also carries a counting wheel 47 provided with teeth which actuate a small electric contact 48. The circuit of this contact operates an appropriate counter such an electronic decimal counter which registers automatically the angular displacement of the exiplorer arm in both directions. lf the signals from the detector 29 are simultaneously registered during this displacement, there is obtained an accurate diagram of the central spot of the sample under test.

Alternately in lieu of the toothed wheel 47 and of the electric contact 48 there may be used a rotating screen as for instance a perforated disc, in association with a photo-electric cell and a corresponding light source. There is thus obtained a counting device which may be operated at much higher speeds. The number of pulses per rotation of the shaft 43 may be greater and any operating error is avoided when the shaft is accidentally rotated at an abnormally high speed.

In order to indicate the angular position of the arm 27 and more particularly the initial position thereof at the beginning of a displacement, there is provided on the extension 35 of the bed 1 a scale 49 adapted to cooperate with an index 5i) provided on the arm. This index may of course be provided with a Vernier.

It is important to note that the frictional transmission between the ribbon 37 and the arm 27 permits of displacing the arm with respect to the ribbon, if desired. Considering FIG. 2 it will be understood that by applying to the surface 44 a sufficiently high lateral pressure, the surface may be caused to slide on the ribbon 37 which is retained by the action of the worm gearings. It is thus possible to bring rapidly the arm at the `approximate angular position desired without having to rely on the quite slow displacement imparted to the arm by the electric motor 45, the latter being only used for the tine adjustment. Further in the device described wear' is automatically compensated by the longitudinal elasticity of the endless ribbon without having to rely on auxiliary systems such as compression springs, adjusting screws, and the like.

We claim:

1. An apparatus for the study of low angle scattering of X-rays by a sample of material, the apparatus including: ya supporting frame; an X-ray source carried by the frame; means on the frame to support the sample to be studied; means supported by the frame to form a substantially monochromatic X-ray beam having a narrow elongated cross-section with a major axis and a minor axis and to direct the beam towards the sample to be studied; an explorer arm mounted for rotation on the frame about an axis positioned close to the sample and substantially parallel to the major axis of an elongated cross-section of the beam; an X-ray detector carried by the arm to receive X-rays diffracted by the sample; with improvements for frictionally driving the arm rotationally about the axis at a slow speed comprising; an arcuate smooth surface carried by the arm concentrically with the axis of rotation of the arm; an endless flexible metallic ribbon in frictional contact with the arcuate surface; rollers rotatably carried by the frame to support the endless flexible metallic ribbon and to maintain the ribbon under tension; and means to rotate at least one of the rollers.

2. An apparatus as in claim 1 further comprising: a common drive shaft rotatably supported by the frame for driving the rollers; worm and wheel reducing gearings connecting the common driving shaft with each of two rollers; and means to rotate the common driving shaft.

3. An apparatus as defined in claim 2 further comprising: a motor shaft rotatably supported by the frame to rotate the common driving shaft; worm and wheel speed reducing gearing connecting the motor shaft with the common driving shaft; and means on the motor shaft to count the angular movement thereof.

4. An apparatus 'as in claim 3 wherein the means on the motor shaft to count the angular advance thereof includes a toothed wheel actuating an electric switching device.

References Cited UNITED STATES PATENTS 8/1953 Good Z50-51.5 4/1958 Henke 259-515 OTHER REFERENCES WILLIAM F. LINDQUIST, Primary Examiner.

RALPH G. NILSON, Examiner. 

